Designing an HVAC system for a building with an indoor swimming pool can be a challenging task for commercial HVAC contractors. This is because indoor pool spaces usually cover a lot of square footage and have very high ceilings. In addition, they have 3 sources of moisture including the pool, intake air, and people using the facility. 

The main goal of the HVAC specialist is to maintain good air quality and provide comfortable conditions for staff, spectators, and swimmers. Something that can only be accomplished by a well-designed air-distribution system with adequate ventilation. Even better, proper air distribution for indoor swimming pools will exhaust toxic chloramines from the pool water and protect the building materials and structure from corrosion and harmful condensation. 


Most indoor and outdoor swimming pools are treated with chlorine. When this chlorine binds to contaminants in the pool water it forms chemicals like trichloramine and dichloramine, which can irritate the eyes and skin. More notably, these chemicals are emitted into the air, where they are corrosive to building materials and toxic to breathe. 

According to the CDC (Center for Disease Control & Prevention), chloramines can build up in the pool water and in the air if there is not adequate fresh air surrounding the pool. This usually happens in indoor pool facilities where the air handling systems aren’t exhausting adequate chloramine-polluted air and bringing in enough fresh air. As a result, the emitted chloramines settle on top of the swimming pool ‘s water surface, where they can have negative health effects on the spectators and swimmers. In addition, chloramine-polluted air corrodes stainless & carbon steel in the facility since it’s acidic, which can cause structural deterioration. 

To get rid of these chloramines and create a healthy indoor pool environment, a ventilation system is needed to circulate enough outdoor air and provide proper air distribution within the facility! 

Air Distribution for indoor swimming pools

As mentioned above, proper air distribution in an indoor pool facility prevents corrosion, condensation as well as temperature & humidity stratification. In addition, it provides effective air mixing throughout the space and removes airborne disinfectant byproducts like chloramines. Not to forget that it will also deliver fresh outdoor air to the spectators, people on the deck as well as swimmers’ breathing zone. 

However, to accomplish all this, a high rate of total movement in the facility is needed. More importantly, the air-distribution system must continuously prevent corrosion, condensation, and stratification, regardless of whether the space is occupied or not, which requires that diffusers supply air effectively. 

On top of that, indoor pool spaces are usually made up of several microzones, including the deck, spectator areas, and the swimming area, all of which need corrosion and condensation prevention. Moreover, these spaces are quite tall as they are about 15 – 50 ft high, and require good air mixing throughout the facility to prevent dead spots and stratification that can cause corrosion. For these reasons, it’s important to have a higher amount of outdoor air in the facility’s total supply-air rate. supply air refers to the total airflow delivered to the indoor pool space, including recirculated air and outdoor air. 

Factors that affect Indoor Air Quality in indoor swimming pool facilities

HVAC designers that follow guidelines in the ASHRAEHanbook should have every expectation of a pleasant indoor pool experience and great space condition. However, there are other steps the HVAC designer must take into consideration to reduce the chances that the swimmers, staff, and spectators experience ill health effects or discomfort. This is because there are several factors that can impact the Indoor Air Quality in indoor pool facilities, including poor air distribution. Other factors that can affect IAQ in these facilities are; poor high humidity, inadequate outdoor air, occupant/ swimmer behavior, air stagnation, facility operation & maintenance, and water chemistry problems. 

Luckily, the 4 key factors that can have the most direct impact on IAQ are under the control of the HVAC design engineer. They include; poor air distribution, outdoor air ventilation, air change rate, and exhaust air. However, other factors that could also have a significant impact and aren’t under the control of HVAC engineers such as pool water maintenance and operation should be addressed by the facility operator. 

  • Supply Air 

The most important focus of the HVAC system design for indoor swimming pool facilities is to provide enough supply air into the breathing zone. An HVAC system conditions the supply air before it’s mixed with filtered outdoor air. The supply air is then delivered down into the breathing zone, ensuring that the patrons enjoy the best possible indoor air quality. 

In addition, a properly designed HVAC system for indoor swimming pool facilities will adequately remove and control chloramines, while providing conditioned and treated air into the deck area and breathing zone. 

  • Air Exchange Rate 

According to ASHRAE, it’s important to have a proper volumetric supply air change rate per hour to ensure that the entire room experiences air movement. Also, this will help to avoid stagnant areas, as they’re prone to air quality problems and condensation. 

At the same time, short-circuiting between return and supply air should also be avoided since it significantly reduces the overall effectiveness of the MEP system and the actual changes within the space. 

Specifically, ASHRAE recommends 6-8 volumetric air change rates per hour and 4 -6 volumetric air change rates per hour in the spectator area and regular natatorium respectively. 

The supply air requirement (CFM) can be quickly determined by multiplying room volume (cubic ft.) by the desired air change divided by 60. 

  • Outdoor Ventilation Air 

Outdoor air in indoor swimming pools plays a critical role in maintaining good IAQ and diluting airborne chemicals. The amount of outdoor air that should be introduced to the indoor swimming pool facility is usually determined by local codes. However, most local codes in the United States adopt ASHRAE Standard 62. Facilities that follow ASHRAE Standard 62 guidelines to introduce outdoor air will have outstanding indoor air quality and effective air distribution. 

  • Exhaust Air 

According to the ASHRAE Handbook, the room should be maintained at 0.05 to 0.15” WC negative pressure depending on the surrounding spaces. In most cases, 10% more exhaust air compared to outdoor air is a good practice. 

However, more exhaust air than proposed by the ASHRAE guidelines will not prevent or reduce the movement of moisture through the building envelope to the outdoors, especially in cold weather. Besides, moisture migrates depending on the vapor pressure differential. On cold winter days, there is an effective pressure difference of about 10” WC between outdoor and indoor spaces. Therefore, no amount of negative air pressure can be added to the space to prevent moisture migration. Instead, this can only be prevented by installing vapor retarders in strategic locations throughout the building envelope. 

In that regard, an indoor swimming pool should have an exhaust air intake grille installed directly above it. That way, the system will capture and extract the highest level of contaminants before they diffuse into the facility and negatively affect indoor air quality. 


Proper air distribution in indoor swimming pools will help everyone breathe a little easier, and make the space healthy for spectators and swimmers. HVAC design engineers at Innodez will help you create the right design and operation for your recreation and sports facility. If you’re planning to build or own an indoor swimming pool facility in California, give us a call today!

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